Various human tissues appearing in a photo-acoustic image have different optical absorption coefficients from each other.
FIG. 1 shows an optical absorption coefficient in a human tissue.
Referring to FIG. 1, each material has a given optical wavelength to output an optimal photo-acoustic coefficient (absorption coefficient) in a human body. For example, Hb shows an optimal optical absorption coefficient near 400 nm and 550 nm, HbO2 and protein shows an optimal optical absorption coefficient near 420 nm, 550 nm and 900 nm, and protein shows an optimal optical absorption coefficient near 200 nm. By discriminating an optical wavelength with an optimal optical absorption coefficient by using such different optical absorption coefficients of materials, a surrounding background and a physiological change of a human body of interest may be discriminated.
If a photo-acoustic imaging technique using an optical absorption coefficient in a human tissue is used, a physiological change in the human body may be imaged using a variation according to each optical wavelength. Meanwhile, even though all tissues react optimally to specific optical wavelengths, they may also react, though not optimal, when imaging another tissue. In other words, all optical absorption coefficients may not be perfectly discriminated, and thus there is needed a method and apparatus for selectively discriminating a background.
Moreover, calcification in the breast and thyroid tissues becomes an important clue in an early diagnosis of cancer. In other words, calcification of a micro scale plays a role of an indicator of cancer occurrence, and thus it is very important to detect a calcified tissue in advance.
An early diagnosis of breast cancer and thyroid cancer is performed by checking calcification by means of mammography or verifying a positive or negative reaction by means of ultrasonic image and biopsy.
In case of the mammography, however, X-ray is excessively irradiated to a human body, a pain caused by compressing is applied to the patient, real-time imaging is not easy, and particularly it is not easily applied to thyroid.
Meanwhile, the ultrasonic image is a non-radiological imaging method which may give an image in real time, and any inconvenience such as compressing is not given to the patient. However, due to low contrast and serious noise in the image, identifiability deteriorates, and thus when guiding a biopsy needle, it is not easy to check an accurate location of a calcified tissue or lesion. Therefore, there is needed a real-time imaging technique capable of further emphasizing an image of a micro-calcified tissue and minimizing a reaction of an image without a calcified tissue.